textproduct: Rapid City

KEY MESSAGES

- Risk for isolated severe storms tomorrow (Friday), mainly across northeastern WY into far western SD. Main hazards will be large hail (1+" in diameter) and damaging wind gusts (60+ mph)

- Risk for scattered severe storms across northwestern SD on Saturday.

DISCUSSION

(This Evening Through Thursday) Issued at 1235 PM MDT Thu Jun 25 2026

Vis/IR satellite imagery depicts clearing skies over our northeastern WY counties with line of storms pushing eastward across northern WY. Further east of this line, isolated convection has begun to develop over the Bighorns. Most recent CAMs show the line of storms pushing eastward into the far western reaches of our CWA by mid- afternoon. Forecast DCAPE of 900-1000 J/kg and somewhat steep 700mb lapse rates of 6-7 C/km will support isolated severe wind and hail potential, mainly across Campbell County. This line should weaken as it moves eastward into SD and while a stronger storm or two can't be ruled out, widespread severe weather is not expected.

Longwave trough pushes into the western US on Friday with zonal westerly flow over our neck of the woods transitioning to southwest flow. Southeast sfc flow will bring warm, moist air into the region with ML CAPE values rising to 1000 to 2000 J/kg across the western half of our CWA by the late afternoon/evening hours. However slight height rises and warm 700 mb temps will likely keep the severe threat conditional for Friday. CAMs show some convection developing over northeastern WY Friday afternoon and moving into western SD by the evening hours. Inverted-V profiles with steep low level lapse rates and high LCLs indicate high based storms with a severe gust threat.

Severe potential continues on Saturday as a shortwave and attendant lee sfc trof/low moves through the region. Current thinking is that as the sfc trof deepens over western SD, axis of 2500-4000 J/kg SB CAPE will develop in the warm sector. Meanwhile, bulk shear of around 30 to 45kt will support rotating updrafts and organized convection. The main question is where the strongest instability and shear will set up, which current model runs are still not in great consensus about. So far, the highest confidence for where severe weather may occur on Saturday is across northwestern SD towards central SD. Confidence decreases closer to the Black Hills and southwestern SD into northeastern WY. Initial convection may start out as discrete supercells with all hazards possible before growing into an MCS with wind and hail becoming the main threats.

Unsettled southwest flow continues over the CWA through Sunday as the western US trof deepens. This will result in chances for storms later Sunday into Monday. Additionally, temperatures will continue to warm through this weekend with highs in the 80s to 90s by Saturday and Sunday. After a slight cool down on Monday, ensemble guidance is signaling much warmer conditions for later next week as a ridge builds over the eastern and central US.

AVIATION

(For the 00Z TAFS Through 00Z Friday Evening) Issued At 541 PM MDT Thu Jun 25 2026

The risk for thunderstorms is diminishing early this evening. Areas high-end MVFR to low-end VFR CIGS will continue to impact portions of northeastern WY/western SD for a few more hours before improving conditions overnight.

A more defined round of thunderstorms will move across northeastern WY starting after 20z tomorrow, moving into the Black Hills early in the evening. Strong erratic winds and local IFR conditions will occur with the strongest storms.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.